Corn to Ethanol Process

7/28/2019 Corn to Ethanol Process

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The Dry Grind Corn to Ethanol Process

TM

National Corn-to-Ethanol Research Center

Southern Illinois University

Education and Workforce Development

400 University Park Drive

Edwardsville, Illinois 62025-3604

Office: (618) 659-6737 ext. 239Fax: (618) 659-8762

www.ethanolresearch.com

A copyright statement is as follows:

----------------------------

Copyright 2007, Board of Trustees of Southern Illinois University, National Corn to Ethanol Research Center,

Edwardsville, Illinois 62026

All rights reserved.

These materials are protected by copyright and may not be reproduced, copied, displayed, or disseminated

in any media without the express consent of the National Corn to Ethanol Research Center

----------------------------


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12

9

13

Yeast

7

Hammer Mill Slurry

Tank JetCooker

CO2

Enzyme

4

Enzyme

4

Fermentation

Denatured

Ethanol Molecular

Sieve

10

Distillation

System

CentrifugeEvaporator(Syrup)Drum Dryer

5Liquefaction

8

9

911

12

3

Dried Distillers

Grain with Solubles

The Corn to Ethanol ProcessNational Corn-to-Ethanol Research Center, SIUE

5%

Gasoline

Added

(200 Proof )

(190 Proof )

(Whole

Stillage)

Start HereAmmonia

Steam

(Recycled Water)

Urea

(Cooling)

( Wet Cake)

(Thin

Stillage)

Water

(Heating)

Enzyme

6

TM

2007 All Rights Reserved


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Midwest Corn typically contains: 70-72% starch, 9% protein, 4% oils, and

9% fiber on a dry basis, plus approximately 15% water.

1

Hopper

Most corn grown for ethanol production is #2 yellow dent corn, so named

because of the indentation that occurs on top after the kernel is allowed

to dry.


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The corn kernels are milled to a coarse flour and passed through a fine

mesh screen.

2

Hammer Mill

The corn particle sizing is a compromise between:

(B) leaving large enough particles for drying the Distillers Grain

at the end for animal feed.

(A) grinding fine enough to provide increased surface area to makestarch granules available for reaction with water and enzymes and


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Slurry

Tank

3AmmoniaorSulfuric Acid

(Recycled Water)

Water

Corn flour from the hammer mill is mixed first in the slurry mixer

with hot water and alpha-amylase enzyme.

The resulting slurry is adjusted to a pH of 5.6 to 6.0 with acid or base.

Hammer Mill

Slurry Mixer

(Corn flour)


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SlurryTank

alpha-

amylase

3

Only one third of the total alpha-amylase is added in the slurry

Tank.

The remaining alpha-amylase will be added later in the

liquefaction tank.

Temperature = 185oF

pH = 5.6 to 6.0% Solids = 32%


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Jet Cooker

Steam

Slurry Mash

The slurry mash is heated to above 220F in a jet cooker using direct

steam.

holding column

Upon exiting the jet cooker, the corn slurry enters a holding column

where the mixture is held for 5 to 10 minutes.


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LiquefactionTank

alpha-amylase

5

From the holding column, the slurry enters a Liquefaction Tank (5).

The jet cooking and liquefaction steps break apart the long starch

granules. The shorter molecules are called dextrin.

holding column

Temperature = 185oF

pH = 5.6 to 6.0% Solids = 30%

Additional alpha-amylase is added and the mash is allowed to react

(liquefy) for approximately 30 minutes.


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Glucose is converted by yeast (7) through a series of multi-step reactions

to ethanol and carbon dioxide in the fermentation tanks (8).

9

CO2

Fermentation

Tanks

SSF

Yeast

7

8

Liquefaction Tank

A second enzyme, gluco-amylase (6), is added to complete the dextrin

breakdown to glucose.

gluco-amylase

6

Temperature = 90oFpH = 3.5 to 4.0

Over the past 10 years, many ethanol plants have started adding the

saccharifying enzyme (gluco-amylase) directly to the fermentation tank.

This faster process is know as Simultaneous Saccharification and

Fermentation (SSF).


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CO2

Carbon dioxide is a major co-product in the fermentation process.

9

Fermentation

Tanks

Every bushel of corn (approximately 56 pounds) will produce

approximately 18 pounds of carbon dioxide gas.


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Yeast can withstand extreme environmental stresses including highethanol concentrations (final concentrations of 12-18% by volume), as

well as organic acids produced by contaminating bacteria. Fortunately,

most bacterial contaminants do not grow below pH 4.

Yeast

7Fermentation

Tanks

Contaminating microorganisms can lower the yield by converting glucoseto some undesirable fermentation products like fusel oils (undesired

alcohols), acetic acid, and lactic acid. Antibiotics maybe added to the

fermentation process to minimize bacterial contamination.


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Distillation System

At the end of fermentation, the product is called beerand contains 12%

or higher concentration of ethanol. The beer is typically stored in a tank

referred to as the beer well.

Beer Well

The distillation system typically consists of three columns.

(beer)


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(gases) M l l Si


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First, the beer is passed through a degassing column (gray) to removecarbon dioxide and other gases.

Distillation SystemBeer Well

Centrifuge

(gases) Molecular Sieve

(whole stillage)

Separation of ethanol/water from the non-converted solids mixture occurs

on the beer column (blue). These non-converted solids (whole stillage)

fall to the bottom and are sent to the centrifuge for separation.

Further separation of the ethanol/water mixture is accomplished using a

rectifier column (red). The 190 proof ethanol is sent through a

molecular sieve column to convert it to 200 proof.


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from Rectifier Column190 Proof


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Conventional distillation methods yield 190 proof (95% pure ethanol)

because ethanol and water form an azeotrope. An azeotropeis simply a

mixture of two substances that form a constant boiling point mixture.

Molecular

Sieve

10

Denatured

Ethanol Tank

from Rectifier Column

200 Proof

190 Proof

Temperature > 280oF

Pressure = 6 psig

The remaining 5% water is removed by molecular sieves, which rely on

pore sizes to separate the smaller water molecules from ethanol.


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Finally, anhydrous (100% or 200 proof) ethanol is denatured, typically

with 5% gasoline to exempt the ethanol from beverage alcohol taxes.

5%

GasolineAdded

Denatured Ethanol

11

Molecular Sieve


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Centrifuge whole stillage

wet cake

thin stillage

The solids materials remaining after distillation of ethanol from the beercolumn is called whole stillage. Whole stillage contains 13-17% solids

and is composed primarily of small particles of corn that did not get

converted to ethanol. This whole stillage is separated in the centrifuge

into wet cake and thin stillage.

Wet cake is a more concentrated form of the whole stillage and

contains approximately 35% solids after leaving the centrifuge. Since it

contains mostly solids, it must be augured or conveyed to the drum

dryer.


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backset


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Evaporator

(syrup)

12Centrifuge

Drum Dryer

backset

(wet cake)

(thin

stillage)

The thin stillage is primarily water with between 4 and 5% solids. The thinstillage is evaporated down to a concentrated syrup in the evaporator.

The condensed water is recycled to the Slurry tank. This condensed

water is called backset and helps to conserve total water usage.

The remaining liquid is concentrated (called syrup) by evaporation and

mixed with the wet cake before entering the dryer. Syrup is

approximately 28-30% solids and contains mostly protein and oils from

the corn. The addition of syrup increases the nutritional value of the

DDG.


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Evaporator


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Rotary Drum DryerDDGS Centrifuge

(wet cake)

Evaporator(syrup)

The mixture of syrup and wet cake is dried to generate Dried Distillers

Dried Grain with Syrup or Solubles (DDGS). DDGS is typically dried to a

10% moisture level.

The moisture content and correspondingly short shelf-life of wet distillers

grains limit use of this feed product to the immediate vicinity of ethanol

plants.

The shelf life of the DDGS can be lengthened by adding organic acids as

preservatives and removing almost all the moisture content.

Inlet Air Temperature = 600-1200oF

DDGS Residence time = approximately 30 minutes


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13

Distillers Dried

Grain with Solubles

In the dry grind process, corn is ground whole and fermented to ethanol.

The only major by-products are ethanol, carbon dioxide, and Distillers

Dried Grain with Solubles.

DDGS is sold primarily as cattle feed.

NCERC


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Hammer Mill

Slurry

Tank JetCooker

Fermentation

Ethanol

StorageMolecular

Sieve

Distillation

System

Evaporator(Syrup)Drum Dryer

Liquefaction

9

9

Centrifuge

DDGS

(200 Proof )

(190 Proof )

Whole

Stillage

(Recycled Water)

(Cooling)

( Wet Cake)

(Thin

Stillage)

(Heating)

TM

Centrifuge

DE

TS %

pH

DE

pH pHHPLC

H2O %

Proximate

Analysis

TS%

Proximates

Amino Acids

Total P

Ash

etc.

HPLC

Particle SizeGrain

Qual

Corn to Ethanol Process

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